The present invention relates to electronic devices, and, more particularly, to semiconductor devices useful in controlling circuitry upon resets such as after power failures and manual overrides.
Power failures for computer systems can lead to loss of all information held in volatile memory, and power surges can damage components. Thus power down and power up routines are typically built into computer systems, and sensors for power failures together with reset signal generators and battery backups are available. For example, Motorola part MC34064 and Mitsumi part PST518 are undervoltage (i.e., power failure) sensors that output a reset signal. These parts rely upon hystersis in the comparator to avoid erratic reset signals.
Similarly, external reset pushbuttons are common for computer systems, but such pushbuttons can bounce and give spurious reset signals that disrupt computer operation. In particular, microprocessors, microcontrollers, and microcomputers typically have only limited or no internal power failure sensors or pushbutton debouncing circuitry, but rather have only a simple reset input and rely upon external information.
The present invention provides a monitor that detects both power failures and pushbutton operation and that provides a reset signal plus a settling time extension of the reset signal.